A search is presented for an extended Higgs sector with two new particles, 𝑋 and 𝜙, in the process 𝑋→𝜙𝜙→(𝛾𝛾)(𝛾𝛾). Novel neural networks classify events with diphotons that are merged and determine the diphoton masses. The search uses LHC proton-proton collision data at √𝑠=13 TeV collected with the CMS detector, corresponding to an integrated luminosity of 138 fb−1. No evidence of such resonances is seen. Upper limits are set on the production cross section for 𝑚𝑋 between 300 and 3000 GeV and 𝑚𝜙/𝑚𝑋 between 0.5% and 2.5%, representing the most sensitive search in this channel.
